With the development of integrated circuits (IC), both AM and FM radio circuits have been integrated into one chip. Conventional radio chips with a frequency scan function implement a frequency-lock-loop in a manner to achieve only a forward (i.e., band-up) electronic tuning function. Such a scan function drives the radio chip, starting at its presently tuned frequency, to a higher frequency by increasing the radio's intermediate frequency. The scan function stops at the next higher transmitting station frequency that is detected and received by the IC radio.
To tune to a station transmitting on a lower frequency a user must perform a complicated process. First, the user must press a reset button which causes the front end of the radio to tune its intermediate frequency for reception of the lowest frequency in the band. Then the user must press the scan button to cause the receiver to increase its intermediate frequency. The tuning will stop at the next received up-band station. Should a user desire to hear a station transmitting at a yet higher frequency, the scan button must be repetitively pressed until the desired station is reached. If the desired station is at the high end of the band, this process can be especially long, drawn out and frustrating to the user. Particularly, if the user begins this complicated process from a station with a frequency slightly up-band from the desired station's frequency.
Missing from the art is an electronic tuning circuit for IC radios which implements a reverse (band-down) search tuning ability. The present invention can satisfy this need.